Variables Affecting the Strength of Bond between Porcelain and Gold

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					        Journal of Dental Research

Variables Affecting the Strength of Bond between Porcelain and Gold
                              Myer H. Lavine and Frederic Custer
                                   J DENT RES 1966 45: 32
                             DOI: 10.1177/00220345660450012501

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Variables Affecting the Strength of Bond
between Porcelain and Gold
Department of Dental Materials, Temple University School of Dentistry,                             Philadelphia, Pennsylvania
                                      SYNOPSIS IN INTERLINGUA
riables demonstrava que si le auro es rendite aspere ante le fusionage de illo con porcellana, un augmento
de inter 13 e 15 pro cento pote esser obtenite in le fortia del ligaminage. Quando le agente Ceramcote de
conditionage de metallo esseva usate a un temperature de 980 C, le fortia del ligaminage cresceva per 6 a
10 pro cento. Tamen, quando Ceramcote esseva cocite a un temperature de 1050 C, un augmento de 25
pro cento esseva necessari in le carga pro effectuar le fracturation del ligaminage. Le utilisation de un vacuo
in le fusionage del porcellana al auro produceva resultatos plus uniforme e un augmento de 11 pro cento in
le fortia del ligaminage in comparation con illo obtenite per le normal processo de fusion.

In recent years, fused porcelain as a restora-                              or show bond separation, or the metal may
tive dental material has been reexamined by                                 display permanent deformation.
many researchers, most of whom think that                                      The investigation of certain manipulative
no other dental material can favorably com-                                 procedures was made so that evaluation
pete with porcelain as to its esthetic quali-                               could be made of those variables that could
ties and compatibility with oral tissues.1' 2                               provide a more optimal bond. These vari-
   The dental profession is in need of a                                    ables were: (a) preheating the metal to
porcelain-fused-to-metal combination that                                   1,800° F. before the addition of porcelain, as
will provide mechanical strength as well as                                 compared to eliminating the preheating; (b)
esthetics for veneers used in fixed partial                                 stone-roughened surface compared to cast
prostheses. The term "mechanical strength"                                  texture; (c) application of a metal condi-
is not used to imply that the porcelain ve-                                 tioner to the castings fired at two different
neer contributes anything more than a cos-                                  temperatures, and (d) vacuum and non-
metic effect to the restoration. The success                                vacuum firing of the porcelain.
of the restoration is dependent on the design
of tooth preparation and the quality of the                                          Materials and Methods
metal backing used in respect to its strength                                   Wax patterns of uniform size (26-gauge
and the thermal coefficient of expansion.3                                   thickness, 5 mm. wide and 30 mm. long)
    Any forces acting on the porcelain-fused-                                were prepared and sprued. The sprued pat-
to-metal combination will result in stresses                                 terns were then invested, using Ceramigold
in the restoration. If the external force is                                 Investment* at a constant liquid-powder
directed at the metal, the resulting stress                                  radio.
within the metal will be transferred through                                    The wax patterns were eliminated by
 the bond to the porcelain or vice versa.4                                   heat, using the investment thermal expan-
    Stress may be caused by (a) cooling or                                   sion technic. The casting rings were heated
heating too rapidly; (b) a great difference                                  slowly for 1 hour to a temperature of 7820 C.
between the temperature coefficient of the                                   (1,350° F.). The hot rings were allowed to
porcelain and metal, and (c) externally ap-                                  heat-soak for 15 minutes at 1,3500 F.
 plied forces resulting from function. During                                   Ceramco No. 1 goldt was melted with an
 function, when excessive forces are directed                                oxygen gas flame and the invested pat-
 at the porcelain, the porcelain will fracture                               terns were cast, using a nonvacuum centrif-
     Presented at the International Association of Dental Re-
 search Meeting, Pittsburgh, Pa., March 21, 1963.                                 *  Whip Mix Corp., Louisville, Ky.
     Received for publication July 24, 1963.                                       t J. F. Jelenko & Co., New Rochelle, N.Y.

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Vtol.   45, No,   I                                    V.ARIABLES AFFECTING PORCEL.4IN FUSED TO GOLD 33
                     TABLEt 1                                                      research is now in progress in an attempt
         IJ)INTIFYING SYMBOLS OF CASTINGS                                          to determine whether oxidation of the metal
                                                                                   is actually taking place. The others were
                                                                                   not subjected to this process. A metal con-
G roup                               Description
                                                                                   ditioner* was used on some of the castings
   A      nouroughened, oxidized.                                                  according to the manufacturer's directions.
   B      nonroughened, oxidized; metal conditioner                                   Opaque porcelain, meeasured by the small
            fired at i 38(s0 F.                                                    aperture of a plastic silicate-cement meas-
   C      roughened, oxilizecl.
   D      roughened, nonoxidized; metal conditioner                                uringy device, was mixed with distilled water
            fired at 1,800° F.                                                     and placed on the 5-mm. by 15-mm. areas.
   E      roughened, oxidized; metal conditioner fired                             Small rectangular pieces of 28-gauge green
            at 1,800hF.                                                            wax were attached to the castings at the
  F       roughened. oxidized; metal conditioner fired                             scratch marks to limit the porcelain to the
            at 1,8000 F., vacuum baked.
   G      roughened, oxidized; metal conditioner fired                             predetermined marked area during vibrat-
            at 1,800° F., multiple vacuum baked.                                   ing condensation (Fig. 2).
   it     roughened, nonoxidized; metal conditioner
            fired at 1,925' F.
   I      roughened, oxidized; metal conditioner fired
            at 1,925°oh .

uagal casting machine. After the casting was
completed, the ring was quenched in water
as soon as the button emitted a dull red
glow. The cast ings were cleaned, using ultra-
sonicnmethods and were inspected for de-
fects that could influence the end result.
   For ty-three individual castings weremneas-
ured and marked 5 mm. and 20 mm. from
the end opposite the sprue end, using a
Boley gauge. Identifying symbols were
placed on the CaStillgS (Table 1). The                                                       FIcG 2.      Firing of the opaque porcelain
marked-off 5-by-15- mm. areas were rough-
ened with a heatless stone or left as they                                             After drying, the wax xvas removed from
were cast (Fig. 1). Thirty-three castings                                          the samples, which. were placed on a silica
were heated to 1,8000 F. in a porcelain oven                                       slatb in a porcelain furnace (preheated to
and kept at that temperature for 20 min-                                           1,200' F.) and kept there for approximately
utes, thereby subjecting them to what we                                           8 minutes, until they were fired to 1,8000 F.
regard as an oxidative-type process. Further                                       After cooling, the body or gingival porcelain
                                                                                   measured by the large aperture of the sili-
                                                                                   cate-cement measuring device was con-
                                                                                   densed on the opaque porcelain and fired in
                                                                                   the same way (Fig. 3).
                                                                                      The testing apparatus (Fig. 4), a modified
                                                                                   form of the transverse tester for denture
                                                                                   base resins in the American Dental Associa-
                                                                                   tion Specification No. 12, was used so that
                                                                                   the porcelain-gold bond would be subjected
                                                                                   to vulnerable tensile stress from increased
                                                                                   bending forces (Fig. 5). The bending forces
                                                                                   would cause the porcelain to separate from
                                                                                   the casting or to fracture. If the bond proved
                                                                                   sufficient, the porcelain would crack (Fig. 6).
                                                                                   The deflections gauge was placed on zero, and
           FIG.   1.--    Preparation of the castings                                   *   Ceramcote, Ceramco, Inct, Woodside, N.Y.

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3-1 LZI 171NE AND CUSTER                                                                     J. dent I. Res. January-Februtary 1066

                 Fusion of 1)0(1)~~~~~~~~~~~~~~~~~~~~~..
              Vie.. .                               .orclai

100 Gm. of shot in a paper                  CuP was placed
on the testing table. At the end of each
Finute a reading of the deflection gauge
     record, ad another 100 Gn of shot
was  ad~ded. 'lhe weight, time and clefiec-
tions were recorded when the sample failed.
   When the roughened, oxidized, condi-
tioned samples (Group E, Table 2) were
compared with the rougyhened, oxidized sam-
ples (Group (7, Table 2), and the smooth,           FI. 'S. A testedl sample showigspraino
oxidized, conditioned samples (Group B,                                the
                                                    jsorcelain from the casting.
Table 2) were compared with the smooth,         oxilizec samples (Group A, TaLblce 2), the
                                                metal conditioner (subjected to 1,St00 F'.
                                                firing) increased the bond strength 10 per
                                                cent,and 6 per cent, respectively. The con-
                                                ditioner sub jectec to l,925' F. firing (Grou1p
                                                I, Table 2), had 24 per cent greater bond
                                                strength than the conditioner subjected to
                                                the 1,800' F. firing (G'roup E, Table 2). The
                                   .h .o ......dbond strength of roughened, metal-condi-
                                                tioned samples fired at 1,925' F. (Group H,
                                               ~~Table 2) had ain increase of 26 per cent when
                                                compared with the roughened, metal condi-
                                                tioned samples fIred at t,8000 F. (Group D,
                                                Table 2). Vacuum baking of the porcelain
                                                (Group F, Table 2) gave 11 per cent grea,~ter
                                                bond strength than the regular backing pro-
                                                                      cedure (GC'roup E, Table 2).
             Wtx- aE                                                          incl
                                                                      firing) bond strength of the samples having
                                                                      the casting  rtiungheied tGi;oup C, Table 2)
                                                                      waIs 13 per cent greater than that of the
                                                                      nonroughened samples (G'roup A, Table 2)
                                                                      xvhen the castings were subjected to heat
                                                                      conditioning. When the metal conditioner
           ie.. 4.- Testing apparatus                                 was added after heat conditioning, the

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Vol. 45, No. I                              VVARIABLES AFFECTING PORCELA IN Ft SED TO GOLD 35


         FIG. 6. -Two samrl-les illustrating separation and cracking of the porcelain, respectively

rotughened samples (Group E, Tal le 2) had operator can, with experience, reduce the
15 per cent greater bondt strength as com-             chances of possible failure if he adheres to
pared with the nonrouighened samples                   the specific instructions of the manufac-
((rotup 13, Table 2). This shows that, in              turer2' If the thermally induced stresses are
this instance, the LISe of metal cotiditioner          eliminated, the success of the restoration is
increased the bond strength by 2 fxer cent.            more dependent on the design of the tooth
                                                       preparation and cast metal framework.
                   Discussion                          Residual stresses are still present but are
    For porcelain-ftfsed-to-metal restedorat ions believed to be minimal.
the maniptlative procedures must b e highly               The manner of testing bond strength
disciplined to achieve satisfactory results. appears to simulate oral conditions. The
The nature of the materials is such that the transverse test is directed to the metal, and
                                                       the resultant forces are directed to the porce-
                      FT\BLE 2                         lain in a tensile stress. Porcelain is known
                                                       to have lesser tensile strength than com-
                                                          The actual deflection of the metal has
                                             Average been established.5 Because gold has an ex-
                                             Load at   tremtely high modulus of elasticity, there
          .No. of    Distribution of        Separation was a minimal amount of deflection. The
 (.roup  Samples             (G m

                                               (Gm.)a length between the supports of the testing
    A\        5   800; 900; 900; 1,000           900   apparatus, the width, and the thickness of
  B           4   900; 1,000; 1,000; 1,100       960   the castings were all constant; actually,
  C           5   1,0(0; 1,000; 1,000;                 therefore, the adhesion of the bond was
                     1tIG0, 1,200             1,040    measured.
    1)        5   800; 900; 1,000; 1,1(1)0;               The thickness of the opaque and gingival
                     1,200; 1,200)
    E         5   900; 1,000; 1,100; 1,200;
                                                 1,060 porcelain could also affect the results; there-
                     1,300; 1,400; 1,500     1,140 nite areaexact was equal to used over athick-
                                                       fore, an
                                                                       amount was
                                                                                     a uniform
    F         5   1,000; 1,100; 1,200;
                     1300; 1,400; 1,500;               ness measured as 1.2 mm. and checked with
                     1,500                   1,28t)    a Boley gauge. The thickness of 1.2 mm.
    G         5   1,200; 1,200; 1,300;                 would be that, of a veneer in the oral cavity.
    H         5
                     1,300; 1,400
                  1,200; 1,300; 1,400;
                                              1,280       The data were subjected to a statistical
                     1,500; 1,600            1,440     analysis of variance that is not includedThe be-
  I           4   1,100; 1,200; 1,300;                 cause of the clinical basis of this report.
                     1,400; 1,500; 1,600;              statistical analysis, however, showed a true
                     1,700; 1,700; 1,800     1t,0o     difference between the different technics

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36 LA VINE AND CUSTER                                                                         J. dent. Res. January-February 1966

                  Summary                                              metal conditioner was fired to 1,9250 F., a
   For good results with porcelain fused to                            25 per cent increase in load was necessary
gold, the technician must be thoroughly                                to fracture the bond.
familiar with the materials, maintain a strict                            This work demonstrated that the most
discipline in manipulating the materials, and                          important factor affecting the strength of
follow the manufacturer's directions in de-                            bond between porcelain and gold was high-
tail.                                                                  temperature firing of the metal conditioner.
   Design of the tooth preparation and the                             Surface roughness and oxidation were lesser
metal restoration or framework are factors                             factors. Additional vacuum-firing trials are
that probably influence the success of                                 needed to prove an influence on bond
the porcelain-fused-to-gold restoration more                           strength due to vacuum firing.
than do the actual materials used.
   By subjecting the gold-porcelain samples                                                        References
to a transverse test, the porcelain actually                            1. DUNSWORTH, F. D. Porcelain Fused to Gold. J. prosth.
was placed under a state of tension, allowing                              Dent., 8:635-39, 1958.
                                                                        2. BRECKEuR, S. C. Improved Porcelain Fused to Gold
measurement of bond strength.                                              Bridges. Dental Clinics of North America, March,
    Roughening the castings before the addi-                               1959, 163-73.
tion of opaque and gingival porcelain re-                               3. SILVER, M. An Evaluation and Comparison of Porce-
                                                                           lains Fused to Cast Metals. J. prosth. Dent., 10:1055-
sulted in 13 to 15 per cent greater bond                                   64, 1960.
strength as compared with nonroughened                                  4. CUSTER, F. The Effect of The Gold Oxidation Process
                                                                           in The Porcelain Fused-to-Gold Bond. Thesis, Uni-
castings.                                                                  versity of Michigan School of Dentistry, 1961.
    The bonding agent fired at 1,8000 F. had                            5. ASGAR, K., PEYTON, F. E. The Effect of Certain Vari-
6 to 10 per cent greater bond strength than                                ables in the Bond Strength of Porcelain Fused to Gold,
                                                                           Abstract M34, read at the annual meeting of the
the castings without the agent. When the                                   International Association for Dental Research, 1962.

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